U.S. Pat. No. 4,536,629 discloses a gas damped deceleration switch having a mass assembly supported in a housing for movement in response to deceleration. The mass assembly is spring biased into a rest position, and is movable against the bias of the spring toward an electrical contact. The electrical contact is movable by the mass assembly to close an electrical circuit to energize an airbag inflator.
The mass assembly comprises a mass and a damping member attached to the mass. The mass is a rod-shaped member having forward and rear ends, and is supported for longitudinal movement in the housing. The damping member is a disk carried coaxially on the mass. Air in the housing exerts a damping force against the damping member when the damping member moves with the mass. The spring is a spiral spring, and is connected to the mass at a position adjacent to the forward end of the mass. The rear end of the mass is supported in a bore formed in the rear wall of the housing, and is slidably movable in the bore. When the deceleration switch experiences a deceleration pulse, the mass assembly moves against the damping force, as well as against the bias of the spiral spring, away from the rest position. If the deceleration pulse is of sufficient magnitude and duration, the moving mass assembly will reach the electrical contact and will move the electrical contact to close the electrical circuit. The airbag inflator will then be energized.
Operation of the deceleration switch can be adjusted by a pair of set screws. Each one of the two set screws is movable axially against a respective one of two spiral arms of the spring to adjust the initial position of the respective spiral arm of the spring when the mass assembly is in the rest position. The set screws thereby apply and adjust separate preloading forces on the spring.